In an emission tomography system, photons from the inside of a body, or in case of system tune-up, from a phantom and the like, that is to be imaged are detected. These photons pass from the interior of the body to a detector outside the body and may be attenuated by different parts of the body, depending on the composition of the body.
In order to reconstruct a three-dimensional distribution of a radionuclide within the body or phantom accurately, this attenuation must be considered. Generally, the emission tomography may be a Positron Emission Tomography (PET), a Single Photon Emission Computed Tomography (SPECT), and the like.
Typically, an emission tomography imaging system must be calibrated. This is usually accomplished using a phantom. The phantom may for example simulate organs or other metabolic active sites of an animal or human body. In a combined MR (magnetic resonance) and emission tomography imaging system, the phantom used for the attenuation correction of an emission tomography subsystem may not be visible in a MR image.